It was a rubber sheet as we thought, and did not hurt the use.
However, when choosing on the site, there was no uniformity in the notation of characteristics, we had to purchase multiple items and compare them. I think that it is kind, if you attach a characteristic data table etc together with goods.

Up to now I bought a disconnected item, but because it can be cut with a cutter, it was purchasing only the material. There is no problem (deterioration) in the result used. I plan to purchase it next time.